This piece of code throws up 'error 380'

Private Sub cbMains8_Change()
cbDish8.RowSource = cbMains8 ' error produced here
cbDish8.ListIndex = -1
End Sub

This piece of code does not throw up an error

Private Sub cbMains7_Change()
cbDish7.RowSource = cbMains7
cbDish7.ListIndex = -1
End Sub

What does error code 380 indicate

TIA

Jim